This invention relates generally to metalworking and more particularly concerns a method and apparatus for finishing a machined workpiece. The invention will be specifically disclosed by way of example, in connection with a deburring or finishing tool used upon a machine tool especially adopted for removing burrs or sharp edges from the interface of two surfaces of a piston ring.
The machining of metals often leaves sharp corners, thin ridges of workpiece material or residual areas of roughness when a metalforming element is removed. Sharp edges are formed whenever two surfaces are machined to abruptly intersect. The thin edges of material and surface irregularities are commonly referred to as burrs.
Burrs may be formed in a variety of ways during a machining process. In general, they are formed whenever workpiece material is permitted to flow unrestrained toward an edge of the metalforming element. They may be produced, inter alia, when a metalforming element enters a workpiece (entrance burrs), when the metalforming element exits the workpiece (roll-over burr), at the edges of the cut (poisson burr) or when a chip is pulled rather than sheared from a workpiece (tear burr).
Whatever the source of burrs or sharp corners, it is imperative that they be removed from many workpieces. The prior art has witnessed a wide variety of deburring techniques. Many of the prior art deburring techniques are multi-step. They require a secondary production step in addition to the primary metalforming process. The expense and time delays precipitated by these multi-step processes make them undesirable from a production viewpoint.
One such commonly employed process involves manually engaging a workpiece with a rotary powered brush after machining. This process, in addition to requiring additional time, is also very frequently ineffective in removing sharp corners.
Another commonly employed technique involves placing a plurality of workpieces into an agitating barrel with abrasive materials. The barrel finishing technique, in addition to being a time consuming second step, is inherently non-selective and may take off critical portions of the workpiece and effect tolerances. Barrel finishing is also generally ineffective in removing burrs from recessed areas.
Abrasive jet blasting is a process in which a compressed air jet stream filled with particulate abrasive matter is directed against a surface. This technique is much more selective than barrel finishing but is unsatisfactory for hard to remove burrs or corners.
Various other deburring techniques have been used in the past, as for example, electro-chemical and thermal deburring. However, like the previously mentioned techniques, they are replete with disadvantages. For example, electro-chemical deburring is expensive and inflexible due to the special tooling required for each different sized workpiece; and thermal deburring may result in damage to the workpiece. Additionally, these techniques, like each of the other aforementioned ones, do not afford the luxury of simultaneously deburring the workpiece with the primary metal forming process.
Mechanical deburring tools do have the potential for simultaneous operation. Still, most prior art mechanical deburring tools have awkward and cumbersome physical structures, a disadvantage which is accentuated when operating upon hard to reach internal surfaces. Further, it has been found that, when using a finishing tool, workpiece material may tend to flow toward the edges of the cut if relative movement between the workpiece and the tool is constant and in a single direction. Thus, many of these tools, when being used to remove a single burr (or ridge) may themselves form a pair of similar, albeit smaller, burrs upon the edge of the workpiece interface. Similarly, a finishing tool which is planar is likely to form smaller burrs at an abrupt edge of the planar surface.